Custom routing decisions

ABSTRACT

With the advent of virtualization technologies, networks and routing for those networks can now be simulated using commodity hardware rather than actual routers. For example, virtualization technologies such as those provided by VMWare, XEN, or User-Mode Linux can be adapted to allow a single physical computing machine to be shared among multiple virtual networks by providing each virtual network user with one or more virtual machines hosted by the single physical computing machine, with each such virtual machine being a software simulation acting as a distinct logical computing system that provides users with the illusion that they are the sole operators and administrators of a given hardware computing resource. In addition, routing can be accomplished through software, providing additional routing flexibility to the virtual network in comparison with traditional routing. As a result, in some implementations, supplemental information other than packet information can be used to determine network routing.

BACKGROUND

Generally described, computing devices utilize a communication network,or a series of communication networks, to exchange data. In a commonscenario, data to be exchanged is divided into a series of packets thatcan be transmitted between a sending computing device and a recipientcomputing device. In general, each packet can be considered to includetwo primary components, namely, control information and payload data.The control information corresponds to information utilized by one ormore communication networks to deliver the payload data. For example,control information can include source and destination networkaddresses, error detection codes, packet sequencing identification, andthe like. Typically, control information is found in packet headers andtrailers included within the packet and adjacent to the payload data.

In practice, in a packet-switched communication network, packets aretransmitted between multiple physical networks, or sub-networks.Generally, the physical networks include a number of hardware devicesthat receive packets from a source network component and forward thepacket to a recipient network component. The packet routing hardwaredevices are typically referred to as routers. Generally described,routers can operate with two primary functions or planes. The firstfunction corresponds to a control plane, in which the router learns theset of outgoing interfaces that are most appropriate for forwardingreceived packets to specific destinations. The second function is aforwarding plane, in which the router sends the received packet to anoutbound interface.

To execute the forwarding plane functionality, routers can maintain aforwarding information base (“FIB”) that identifies, among other packetattribute information, destination information for at least a subset ofpossible network addresses, such as Internet Protocol (“IP”) addresses.In a typical embodiment, the FIB corresponds to a table of valuesspecifying network forwarding information for the router. Meanwhile, toexecute control plane functionality, routers can maintain a routinginformation base (“RIB”) that identifies routes through the network. TheRIB can also contain metrics associated with those routes. As the routerreceives route updates, the router can update the RIB with announced orwithdrawn routes. Generally, where the RIB identifies available routes,the FIB identifies an output interface corresponding to a selected routeand the FIB is typically generated from information in the RIB.

BRIEF DESCRIPTION OF THE DRAWINGS

Throughout the drawings, reference numbers are re-used to indicatecorrespondence between referenced elements. The drawings are provided toillustrate embodiments of the inventions described herein and not tolimit the scope thereof.

FIG. 1 is a network diagram illustrating an embodiment of an overlaynetwork manager (ONM) system for managing computing nodes associatedwith a virtual computer network;

FIG. 2 illustrates a more detailed implementation of the ONM system ofFIG. 1 supporting logical networking functionality;

FIG. 3 illustrates an example embodiment of a substrate networkconfiguration having a route manager capable of determining routes forvirtual networks;

FIGS. 4A and 4B illustrate a virtual network and corresponding substratenetwork where substrate routing is independently determined from virtualrouting;

FIGS. 5A and 5B illustrate a virtual route selection propagated to thesubstrate network;

FIG. 6 illustrates an example substrate network wherein a networktranslation device determines routes into or out of a virtual network;

FIG. 7A illustrates a flow diagram for a process of propagating virtualroutes to a substrate network; and

FIG. 7B illustrates a flow-diagram for a process of determiningsubstrate routing based on target performance characteristics of theassociated virtual network.

DETAILED DESCRIPTION

With the advent of virtualization technologies, networks and routing forthose networks can now be simulated using commodity hardware rather thanactual routers. For example, virtualization technologies can be adaptedto allow a single physical computing machine to be shared among multiplevirtual networks by hosting one or more virtual machines on the singlephysical computing machine. Each such virtual machine can be a softwaresimulation acting as a distinct logical computing system that providesusers with the illusion that they are the sole operators andadministrators of a given hardware computing resource. In addition, asrouting can be accomplished through software, additional routingflexibility can be provided to the virtual network in comparison withtraditional routing. As a result, in some implementations, supplementalinformation other than packet information can be used to determinenetwork routing.

In this disclosure, techniques are described for providing logicalnetworking functionality for managed computer networks, such as forvirtual computer networks that are provided on behalf of users or otherentities. In at least some embodiments, the techniques enable a user toconfigure or specify a network topology, routing costs, and/or routingpaths for a virtual or overlay computer network including logicalnetworking devices that are each associated with a specified group ofmultiple physical computing nodes. With the network configurationspecified for a virtual computer network, the functionally and operationof the virtual network can be simulated on physical computing nodesoperating virtualization technologies. In some embodiments, multipleusers or entities (e.g. businesses or other organizations) can accessthe system as tenants of the system, each having their own virtualnetwork in the system. In one embodiment, a user's access and/or networktraffic is transparent to other users. For example, even though physicalcomponents of a network may be shared, a user of a virtual network maynot see another user's network traffic on another virtual network ifmonitoring traffic on the virtual network.

By way of overview, FIGS. 1 and 2 discuss embodiments wherecommunications between multiple computing nodes of the virtual computernetwork emulate functionality that would be provided by logicalnetworking devices if they were physically present. In some embodiments,some or all of the emulation are performed by an overlay network managersystem. FIGS. 2-4B and 7B discuss embodiments where substrate routingdecisions can be made independently of any simulated routing in theoverlay network, allowing, for example, optimization of traffic on thesubstrate network based on information unavailable to a virtual networkuser. FIGS. 5A-7A discuss embodiments where routing decisionsimplemented on the virtual or overlay network are propagated to thesubstrate network. Thus, a user can specify cost functions for theoverlay network that can be used to make routing decisions in thesubstrate network.

Overlay Network Manager

FIG. 1 is a network diagram illustrating an embodiment of an overlaynetwork manager system (ONM) for managing computing nodes associatedwith a virtual computer network. Virtual network communications can beoverlaid on one or more intermediate physical networks in a mannertransparent to the computing nodes. In this example, the ONM systemincludes a system manager module 110 and multiple communication managermodules 109 a, 109 b, 109 c, 109 d, 150 to facilitate the configuringand managing communications on the virtual computer network.

The illustrated example includes an example data center 100 withmultiple physical computing systems operated on behalf of the ONMsystem. The example data center 100 is connected to a global internet135 external to the data center 100. The global internet can provideaccess to one or more computing systems 145 a via private network 140,to one or more other globally accessible data centers 160 that each havemultiple computing systems, and to one or more other computing systems145 b. The global internet 135 can be a publicly accessible network ofnetworks, such as the Internet, and the 1private network 140 can be anorganization's network that is wholly or partially inaccessible fromcomputing systems external to the private network 140. Computing systems145 b can be home computing systems or mobile computing devices thateach connects directly to the global internet 135 (e.g., via a telephoneline, cable modem, a Digital Subscriber Line (“DSL”), cellular networkor other wireless connection, etc.).

The example data center 100 includes a number of physical computingsystems 105 a-105 d and 155 a-155 n, as well as a Communication Managermodule 150 that executes on one or more other computing systems tomanage communications for the associated computing systems 155 a-155 n.The example data center further includes a System Manager module 110that executes on one or more computing systems. In this example, eachphysical computing system 105 a-105 d hosts multiple virtual machinecomputing nodes and includes an associated virtual machine (“VM”)communication manager module (e.g., as part of a virtual machinehypervisor monitor for the physical computing system). Such VMcommunications manager modules and VM computing nodes include VMCommunication Manager module 109 a and virtual machines 107 a on hostcomputing system 105 a, and VM Communication Manager module 109 d andvirtual machines 107 d on host computing system 105 d. Physicalcomputing systems 155 a-155 n do not execute any virtual machines inthis example, and thus can each act as a computing node that directlyexecutes one or more software programs on behalf of a user. TheCommunication Manager module 150 that manages communications for theassociated computing systems 155 a-155 n can have various forms, suchas, for example, a proxy computing device, firewall device, ornetworking device (e.g., a switch, router, hub, etc.) through whichcommunications to and from the physical computing systems travel. Inother embodiments, all or none of the physical computing systems at thedata center host virtual machines.

This example data center 100 further includes multiple physicalnetworking devices, such as switches 115 a-115 b, edge router devices125 a-125 c, and core router devices 130 a-130 c. Switch 115 a is partof a physical sub-network that includes physical computing systems 105a-105 c, and is connected to edge router 125 a. Switch 115 b is part ofa distinct physical sub-network that includes physical computing systems105 d and 155 a-155 n, as well as the computing systems providing theCommunication Manager module 150 and the System Manager module 110, andis connected to edge router 125 b. The physical sub-networks establishedby switches 115 a-115 b, in turn, are connected to each other and othernetworks (e.g., the global internet 135) via an intermediateinterconnection network 120, which includes the edge routers 125 a-125 cand the core routers 130 a-130 c. The edge routers 125 a-125 c providegateways between two or more sub-networks or networks. For example, edgerouter 125 a provides a gateway between the physical sub-networkestablished by switch 115 a and the interconnection network 120, whileedge router 125 c provides a gateway between the interconnection network120 and global internet 135. The core routers 130 a-130 c managecommunications within the interconnection network 120, such as byrouting or otherwise forwarding packets or other data transmissions asappropriate based on characteristics of such data transmissions (e.g.,header information including source and/or destination addresses,protocol identifiers, etc.) and/or the characteristics of theinterconnection network 120 itself (e.g., routes based on the physicalnetwork topology, etc.).

The System Manager module 110 and Communication Manager modules 109, 150can configure, authorize, and otherwise manage communications betweenassociated computing nodes, including providing logical networkingfunctionality for one or more virtual computer networks that areprovided using the computing nodes. For example, Communication Managermodule 109 a and 109 c manages associated virtual machine computingnodes 107 a and 107 c and each of the other Communication Managermodules can similarly manage communications for a group of one or moreother associated computing nodes. The Communication Manager modules canconfigure communications between computing nodes so as to overlay avirtual network over one or more intermediate physical networks that areused as a substrate network, such as over the interconnection network120.

Furthermore, a particular virtual network can optionally be extendedbeyond the data center 100, such as to one or more other data centers160 which can be at geographical locations distinct from the first datacenter 100. Such data centers or other geographical locations ofcomputing nodes can be inter-connected in various manners, including viaone or more public networks, via a private connection such as a director VPN connection, or the like. In addition, such data centers can eachinclude one or more other Communication Manager modules that managecommunications for computing systems at that data. In some embodiments,a central Communication Manager module can coordinate and managecommunications among multiple data centers.

Thus, as one illustrative example, one of the virtual machine computingnodes 107 a 1 on computing system 105 a can be part of the same virtuallocal computer network as one of the virtual machine computing nodes 107d 1 on computing system 105 d. The virtual machine 107 a 1 can thendirect an outgoing communication to the destination virtual machinecomputing node 107 d 1, such as by specifying a virtual network addressfor that destination virtual machine computing node. The CommunicationManager module 109 a receives the outgoing communication, and in atleast some embodiments determines whether to authorize the sending ofthe outgoing communication. By filtering unauthorized communications tocomputing nodes, network isolation and security of entities' virtualcomputer networks can be enhanced.

The Communication Manager module 109 a can determine the actual physicalnetwork location corresponding to the destination virtual networkaddress for the communication. For example, the Communication Managermodule 109 a can determine the actual destination network address bydynamically interacting with the System Manager module 110, or can havepreviously determined and stored that information. The CommunicationManager module 109 a then re-headers or otherwise modifies the outgoingcommunication so that it is directed to Communication Manager module 109d using an actual substrate network address.

When Communication Manager module 109 d receives the communication viathe interconnection network 120, it obtains the virtual destinationnetwork address for the communication (e.g., by extracting the virtualdestination network address from the communication), and determines towhich virtual machine computing nodes 107 d the communication isdirected. The Communication Manager module 109 d then re-headers orotherwise modifies the incoming communication so that it is directed tothe destination virtual machine computing node 107 d 1 using anappropriate virtual network address for the virtual computer network,such as by using the sending virtual machine computing node 107 a 1'svirtual network address as the source network address and by using thedestination virtual machine computing node 107 d 1's virtual networkaddress as the destination network address. The Communication Managermodule 109 d then forwards the modified communication to the destinationvirtual machine computing node 107 d 1. In at least some embodiments,before forwarding the incoming communication to the destination virtualmachine, the Communication Manager module 109 d can also performadditional steps related to security.

Further, the Communication Manager modules 109 a and/or 109 c on thehost computing systems 105 a and 105 c can perform additional actionsthat correspond to one or more logical specified router devices lyingbetween computing nodes 107 a 1 and 107 c 1 in the virtual networktopology. For example, the source computing node 107 a 1 can direct apacket to a logical router local to computing node 107 a 1 (e.g., byincluding a virtual hardware address for the logical router in thepacket header), with that first logical router being expected to forwardthe packet to the destination node 107 c 1 via the specified logicalnetwork topology. The source Communication Manager module 109 a receivesor intercepts the packet for the logical first router device and canemulate functionality of some or all of the logical router devices inthe network topology, such as by modifying a TTL (“time to live”) hopvalue for the communication, modifying a virtual destination hardwareaddress, and/or otherwise modify the communication header.Alternatively, some or all the emulation functionality can be performedby the destination Communication Manager module 109 c after it receivesthe packet.

By providing logical networking functionality, the ONM system providesvarious benefits. For example, because the various Communication Managermodules manage the overlay virtual network and can emulate thefunctionality of logical networking devices, in certain embodimentsspecified networking devices do not need to be physically implemented toprovide virtual computer networks, allowing greater flexibility in thedesign of virtual user networks. Additionally, correspondingmodifications to the interconnection network 120 or switches 115 a-115 bare generally not needed to support particular configured networktopologies. Nonetheless, a particular network topology for the virtualcomputer network can be transparently provided to the computing nodesand software programs of a virtual computer network.

Logical/Virtual Networking

FIG. 2 illustrates a more detailed implementation of the ONM system ofFIG. 1 supporting logical networking functionality. The ONM systemincludes more detailed embodiments of the ONM System Manager and ONMCommunication Manager of FIG. 1. In FIG. 2, computing node A is sendinga communication to computing node H, and the actions of the physicallyimplemented modules 210 and 260 and devices of network 250 in actuallysending the communication are shown, as well as emulated actions of thelogical router devices 270 a and 270 b in logically sending thecommunication.

In this example, computing nodes A 205 a and H 255 b are part of asingle virtual computer network for entity Z. However, computing nodescan be configured to be part of two distinct sub-networks of the virtualcomputer network and the logical router devices 270 a and 270 b separatethe computing nodes A and H in the virtual network topology. Forexample, logical router device J 270 a can be a local router device tocomputing node A and logical router device L 270 b can be a local routerdevice to computing node H.

In FIG. 2, computing nodes A 205 a and H 255 b includes hardwareaddresses associated with those computing nodes for the virtual computernetwork, such as virtual hardware addresses that are assigned to thecomputing nodes by the System Manager module 290 and/or theCommunication Manager modules R 210 and S 260. In this example,computing node A has been assigned hardware address “00-05-02-0B-27-44,”and computing node H has been assigned hardware address“00-00-7D-A2-34-11.” In addition, the logical router devices J and Lhave also each been assigned hardware addresses, which in this exampleare “00-01-42-09-88-73” and “00-01-42-CD-11-01,” respectively, as wellas virtual network addresses, which in this example are “10.0.0.1” and“10.1.5.1,” respectively. The System Manager module 290 maintainsprovisioning information 292 that identifies where each computing nodeis actually located and to which entity and/or virtual computer networkthe computing node belongs.

In this example, computing node A 205 a first sends an addressresolution protocol (ARP) message request 222-a for virtual hardwareaddress information, where the message is expected to first pass througha logical device J before being forwarded to computing node H.Accordingly, the ARP message request 222-a includes the virtual networkaddress for logical router J (e.g., “10.0.0.1”) and requests thecorresponding hardware address for logical router J.

Communication Manager module R intercepts the ARP request 222-a, andobtains a hardware address to provide to computing node A as part ofspoofed ARP response message 222-b. The Communication Manager module Rcan determine the hardware address by, for example, looking up varioushardware address information in stored mapping information 212, whichcan cache information about previously received communications.Communication Manager module R can communicate 227 with the SystemManager module 290 to translate the virtual network address for logicalrouter J.

The System Manager module 290 can maintain information 294 related tothe topology and/or components of virtual computer networks and providethat information to Communication Manager modules. The CommunicationManager module R can then store the received information as part ofmapping information 212 for future use. Communication Manager module Rthen provides computing node A with the hardware address correspondingto logical router J as part of response message 222-b. While request222-a and response message 222-b actually physically pass betweencomputing node A and Communication Manager module R, from the standpointof computing node A, its interactions occur with local router device J.

After receiving the response message 222-b, computing node A 205 acreates and initiates the sending of a communication 222-c to computingnode H 255 b. From the standpoint of computing node A, the sentcommunication will be handled as if logical router J 270 a werephysically implemented. For example, logical router J could modify theheader of the communication 265 a and forward the modified communication265 b to logical router L 270 a, which would similarly modify the headerof the communication 265 b and forward the modified communication 265 cto computing node H. However, communication 222-c is actuallyintercepted and handled by Communication Manager module R, whichmodifies the communication as appropriate, and forwards the modifiedcommunication over the interconnection network 250 to computing node Hby communication 232-3. Communication Manager module R and/orCommunication Manager module S may take further actions in this exampleto modify the communication from computing node A to computing node H orvice versa to provide logical networking functionality. For example,Communication Manager module S can provides computing node H with thehardware address corresponding to logical router L as part of responsemessage 247-e by looking up the hardware address in stored mappinginformation 262. In one embodiment, a communication manager or computingnode encapsulates a packet with another header or label where theadditional header specifies the route of the packet. Recipients of thepacket can then read the additional header and direct the packetaccordingly. A communication manager at the end of the route can removethe additional header.

A user or operator can specify various configuration information for avirtual computer network, such as various network topology informationand routing costs associated with the virtual 270 a, 270 b and/orsubstrate network 250. In turn, the ONM System Manager 290 can selectvarious computing nodes for the virtual computer network. In someembodiments, the selection of a computing node can be based at least inpart on a geographical and/or network location of the computing node,such as an absolute location or a relative location to a resource (e.g.,other computing nodes of the same virtual network, storage resources tobe used by the computing node, etc.). In addition, factors used whenselecting a computing node can include: constraints related tocapabilities of a computing node, such as resource-related criteria(e.g., an amount of memory, an amount of processor usage, an amount ofnetwork bandwidth, and/or an amount of disk space), and/or specializedcapabilities available only on a subset of available computing nodes;constraints related to costs, such as based on fees or operating costsassociated with use of particular computing nodes; or the like.

Route Selection on Substrate Network

FIG. 3 illustrates an example embodiment of a substrate network 300having a route manager 336 capable of determining routes for overlaynetworks. The substrate network 300 can be composed of one or moresubstrate components or nodes, such as computing nodes, routing nodes,communication links or the like. In FIG. 3, the substrate network 300includes computing nodes A 302, B 304, C 306, and D 308, which arecapable of simulating various components of one or more associatedoverlay networks. The nodes can be located on the same data center or inmultiple data centers. Computing node A is interconnected to node B vianetwork W 310, node B is connected to node C by network X 312, node C isconnected to node D by network Y 314, and node D is connected to node Aby network Z 316. Networks W, X, Y, and Z can include one or morephysical networking devices, such as routers, switches, or the like, andcan include private or public connections. Components shown in FIG. 3,such as the computing nodes and communication manager modules, canimplement certain of the features of embodiments described above withrespect to FIGS. 1 and 2.

In FIG. 3, nodes A 302, B 304, C 306, and D 308 are associated with arespective Communication Manager module 320, 322, 324, and 326. Thecommunication manager modules can implement certain of the featuresdescribed in the Communication Manager 150, 210, 260 and VMCommunication manager 109 a, 109 b, 109 c, 109 d of FIGS. 1 and 2. Forexample, the Communication Manager module 320 for node A can operate ona hypervisor monitor of the computing node and can direct thecommunication of one or more virtual computing nodes 330, 332, 334 ofnode A. The computing nodes, communication managers and Route Manager336 can be part of the same ONM system. In one embodiment, the computingnodes run the XEN operating system (OS) or similar virtualization OS,with the communication managers operating on domain 0 or the first OSinstance and the virtual computing nodes being domain U or additional OSinstances.

The communication manager modules in FIG. 3 are in communication with aRoute Manager module 336, operating on one or more computing devices,that directs routing for the substrate network 300. In one embodiment,the Route Manager operates as part of the ONM System Manager module 110,290 of FIGS. 1 and 2, with functionally combined into a single module.The Route Manager can be located within a data center or at a regionallevel and direct traffic between data centers. In one embodiment,multiple Route Managers can operate in a distributed manner tocoordinate routing across multiple data centers.

In FIG. 3, two virtual networks are associated with the substratenetwork 300. Virtual network 1 (VN1) has components 338, 340, 342,associated with virtual computing nodes on computing nodes A 302, B 304,and C 306. Virtual network 2 (VN2) has components 344, 346, 348associated with virtual computing nodes on nodes A, C, and D 308.

As the Routing Manager module 336 directs network traffic on thesubstrate network 300, traffic can be directed flexibly and variousnetwork configurations and network costs can be considered. For example,routing paths can be determined based on specified performance levelsfor the virtual networks. In one embodiment, if the user for VN1 isentitled to a higher service level, such as for faster speed (e.g. lowerlatency and/or higher bandwidth), traffic associated with VN1 can berouted on a “fast” path of the substrate network 300. For example, inone embodiment, traffic for “platinum” users is prioritized over trafficfor “gold” and “silver” users, with traffic from “gold” usersprioritized over “silver” users. In one embodiment, at least somepackets of the user with the higher service level are prioritized overpackets of a user with a lower service level, for example, during timesof network congestion. The user may be entitled to a higher levelbecause the user has purchased the higher service level or earned thehigher service level through good behavior, such as by paying bills,complying with the operator's policies and rules, not overusing thenetwork, combinations of the same, or the like.

The Route Manager 336 can store user information or communicate with adata store containing user information in order to determine the targetperformance level for a virtual network. The data store can beimplemented using databases, flat files, or any other type of computerstorage architecture and can include user network configuration, paymentdata, user history, service levels, and/or the like. Typically, theRoute Manager will have access to node and/or link characteristics forthe substrate nodes and substrate links collected using various networkmonitoring technologies or routing protocols. The Route Manager can thenselect routes that correspond to a selected performance level for thevirtual network and send these routes to the computing nodes. Forexample, network W 310 and Y 312 can be built on fiber optic lines whilenetwork Y 314 and Z 316 are built on regular copper wire. The RouteManager can receive network metrics data and determine that the opticallines are faster than the copper wires (or an administrator candesignate the optical lines as a faster path). Thus, the Route Manager,in generating a route between node A 302 and node C 306 for “fast” VN1traffic, would select a path going through network W and Y (e.g., pathA-B-C).

In another situation, where the user for VN2 is not entitled to a higherservice level, VN2 traffic from node A 302 to node B 306 can be assignedto a “slow” or default path through network Y 314 and Z 316 (e.g. pathA-D-C). In order to track routing assignments, the Routing Manager canmaintain the routes and/or route association in a data store, such as aRouting Information Base (RIB) or routing table 350. The Route Managercan also track the target performance criteria 351 associated with aparticular virtual network.

In order to direct network traffic on the substrate network 300, theRouting Manager 336 can create forwarding entries for one or more of theCommunication Manager modules 320, 322, 324, 326 that direct how networktraffic is routed by the Communication Manager. The CommunicationManager modules can store those entries in forwarding tables 352, 354,356, or other similar data structure, associated with a CommunicationManager. For example, for VN1, the Route Manager can generate a controlsignal or message, such as a forwarding entry 358, that directs VN1traffic received or generated on node A 302 through network W 310 (onpath A-B-C). Meanwhile, for VN2, the Route Manager can generate acontrol signal or message, such as a forwarding entry 360, which directstraffic received on node A through network Z. The Route Manager can sendthese forwarding entries to the node A Communication Manager 320, whichcan store them on its forwarding table 352. Thus, network trafficassociated with VN1 and VN2, destined for node C 306 received orgenerated on node A can travel by either path A-B-C or path A-D-C basedon the designated performance level for VN1 and VN2.

While the example of FIG. 3 depicts only two virtual networks, the RouteManager 336 can similarly generate and maintain routes for any number ofvirtual networks. Likewise, the substrate network 300 can include anynumber of computing nodes and/or physical network devices. Routes can bedetermined based on multiple performance criteria, such as networkbandwidth, network security, network latency, and network reliability.For example, traffic for a virtual network suspected of being used forspamming (e.g. mass advertisement emailing) can be routed throughnetwork filters and scanners in order to reduce spam.

FIGS. 4A and 4B illustrate a virtual network 401 and correspondingsubstrate network 402 where substrate routing is independentlydetermined from virtual routing. FIG. 4A illustrates a virtual networkincluding several virtual network components. Virtual computing nodes I4404 and I5 406 are connected to a logical router 408. The logical routercan implement certain of the features described in the logical router270 a, 270 b of FIG. 2. The logical router is connected to firewalls I1410 and I2 412. The logical router is configured to direct traffic fromI5 to I2 and I4 to I2, as would be the case if I2 were a backupfirewall. The forwarding table associated with logical router 409reflects this traffic configuration. I1 and I2 are connected to a secondrouter 414. The second router is connected to another virtual computingnode, I3 415. Thus, based on the topology and associated forwardingtable of the virtual network 401, traffic from I4 and I5 to I3 passedthrough I2.

Meanwhile, FIG. 4B illustrates an example topology of the substratenetwork 402 associated with the virtual network 401. The substratenetwork includes computing node A 420, computing node B, and a RouteManager 424. Substrate nodes A and B are each associated with aCommunication Manager 426, 428. Node A is simulating the operation ofvirtual components I2, I3 and I5 while Node B is simulating theoperation of virtual components on I1 and I4 on their respective virtualmachines. The Route Manager can then use information regarding theassignments of virtual components to computing nodes to optimize orotherwise adjust routing tables for the substrate network. The RouteManager can receive such information from the Communication Managersand/or the System Manager. For example, assuming I1 and I2 are identicalvirtual firewalls, the Route Manager can determine that because I5 andI2 are located on the same computing node, while I4 and I1 are locatedon the other node, virtual network traffic can be routed from I5 to I2and from I4 to I1 without leaving the respective computing node, thusreducing traffic on the network. Such a configuration is reflected inthe illustrated forwarding tables 430, 432 associated with theCommunication Managers. Thus, routes on the substrate network can bedetermined independently of virtual network routes.

In some embodiments, the Route Manager 424 or System Manager canoptimize or otherwise improve network traffic using other techniques.For example, with reference to FIGS. 4A and 4B, another instance of I3can be operated on node B 422, in addition to the instance of I3 on nodeA. Thus, virtual network traffic from I5-I2-I3 and I4-I1-I3 can remainon the same computing node without having to send traffic betweencomputing nodes A and B. In one embodiment, substrate traffic can beoptimized or otherwise improved without having different forwardingentries on the substrate and the virtual network. For example, withreference to FIG. 4B, I4 can be moved from computing node B 422 to nodeA 420, thus allowing virtual traffic from I5 and I4 to I2 to remain onthe same computing node. In this way, a user monitoring traffic onlogical router 408 would see that traffic is flowing according theforwarding table in the router, that is, substrate routing istransparent to the user. Other techniques for optimizing traffic bychanging the association of virtual components with virtual machinesand/or duplicating components can also be used.

In some situations, it can be desired that substrate routes reflectroutes specified in the virtual table. For example, the virtual networkuser can wish to control how traffic is routed in the substrate network.However, rather than giving the user access to the substrate network,which could put other users at risk or otherwise compromise security, adata center operator can propagate network configuration or virtualnetwork characteristics specified by the user for the virtual network tothe substrate network. This propagated data can be used in generatingrouting paths in the substrate network, thus allowing the user to affectsubstrate routing without exposing the substrate layer to the user.

Route Selection on Overlay/Virtual Network

FIGS. 5A and 5B illustrate a virtual route selection propagated to thesubstrate network. FIG. 5A illustrates a virtual network topology wherelogical network 1 (LN1) 502 is connected to logical network 2 (LN2) 504and logical network 3 (LN3) 506 by a logical router 508. The currentpreferred routing path specified by the user is from LN1 to LN2.

A user may wish to specify a route for various reasons. For example,routing costs through LN2 can be cheaper than LN3, such as when LN2 andLN3 are in different locations with different ISPs and one ISP chargeslower rates than another. In another example, LN3 can be a backupvirtual network for LN2, and used only in some situations, such as forhandling overflow from LN2.

Referring back to FIG. 5A, the user can specify preferred routes throughthe virtual network and/or characteristics or costs associated with thevirtual components, such as monetary costs, packet loss rates,reliability rate, and/or other metrics. These characteristics can beassigned to the virtual components, such as the virtual computing nodes,node links, logical routers/switches or the like. The Route Manager 510can then determine routing tables 512 and/or forwarding tables 514 forthe virtual network.

FIG. 5B illustrates an example of a substrate route that can correspondto the virtual route in FIG. 5A. In the figure, there are three datacenters 520, 522, 524 corresponding to the logical networks 502, 504,506 of FIG. 5A. In data center 1 (DC1), a computing node 526 isconnected to a network translation device A (NTD A) 528 and a networktranslation device B (NTD B) 530. The network translation devices areconnected to external networks C 532 and D 534, respectively.

The network translation devices can serve as a gateway or entry/exitpoint into the virtual network. In some embodiments, the networktranslation devices can translate between a first addressing protocoland a second addressing protocol. For example, if the virtual network isusing IPv6 and the external networks are using IPv4, the networktranslation devices can translate from one addressing protocol to theother for traffic in either direction. In one embodiment, users connectfrom their private networks to the data centers via a VPN or otherconnection to a network translation device, which translates and/orfilters the traffic between networks.

Referring back to FIG. 5B, network C 532 connects data center 2 522 toNTD A 528. Network D 534 connects data center 3 524 to NTD B 530. TheRoute Manager module 510 is in communication with data center 1 520,data center 2 522, and data center 3 524, particularly with theCommunication Manager for the computing node 526.

From information associated with the virtual network, the Route Manager510 can determine that the user wants to route traffic from LN1 to LN2.The Route Manager can then “favor” substrate routes associated with theLN1 to LN2 virtual path. For example, the Route Manager can specify alow routing cost (e.g. cost 1) for communications, such as data packets,travelling on Network C relative to Network D (e.g. cost 10) such thatduring route determination, routes through Network C are favored. In oneembodiment, the Route Manager can apply a coefficient to storedsubstrate costs in order to favor one route over another. In anotherexample, explicit routing paths can be set up corresponding to thevirtual route. The Route Manager can identify routes in its routingtable and communicate those routes with one or more CommunicationManagers.

Referring back to FIG. 5B, when the computing node 526 receives orgenerates a packet destined for LN2 or a network reachable from LN2, thecomputing node can be configured by the Route Manager to send packetsthrough NTD A 528 as it lies on the route including network C 532.

By propagating virtual network configuration data to the substrate, andusing that configuration data in substrate route calculation, amechanism is provided for a virtual network user to affect substraterouting. In some embodiments, the virtual configuration data can be usedin determining association of the virtual components with the substratecomponents. For example, components of the same virtual network can beassociated with the same substrate computing node or on computing nodesconnected to the same switch in order to minimize or otherwise improvesubstrate network traffic. Configuration data can also be provided theother way and, in some embodiments, the user and/or virtual network canbe provided with additional substrate information, such ascharacteristics of the underlying associated substrate components (e.g.performance, costs) in order to make more informed routing decisions.

FIG. 6 illustrates an example substrate network wherein a networktranslation device determines routes into or out of a virtual network.In FIG. 6, a communication, such as a data packet, leaves computing nodeA, which is associated with a virtual network, through NTD B 604. Thenetwork translation device can include a Route Determination module 605for determining the packet route. NTD B is connected to network C 606and network D 608.

In FIG. 6, the Route Manager 610 receives a network configuration ordetermines that route A-B-C is preferred or has a cheaper cost. TheRoute Manager can store the route in a routing table 612. The RouteManager can then send forwarding entries to the NTD B 604 that configureit to send traffic through network C 606. NTD B can contain multipleforwarding entries for multiple virtual networks, such that data for onevirtual network can be sent through network C, while another virtualnetwork sends data through network D. In some cases, network packetswith the same source and/or destination are sent by different networksbased on the associated virtual network.

In some embodiments, the substrate component may not have aCommunication Manager or a Route Determination module and other ways ofcoordinating routing can be used. For example, a substrate component,such as an ordinary router or a network translation device, can be setup multiply on separate paths. Using blacklists, network traffic for aparticular virtual network can be allowed on one path but blocked onothers. The Route Manager can send a control signal or message updatingthe blacklists to manage the data flow.

In other embodiments, substrate components can implement IP aliasing,where, for example, “fast” path packets use one set of IP addresses,while “slow” path packets use another set of IP addresses. When thesubstrate component receives the packet, it can determine which path touse based on the IP address. The Route Manager can send a control signalor message to assign IP addresses to the components based on the type oftraffic handled.

Other ways of differentiating how packets are handled by substratecomponents include: tagging of packets, such as by Multiprotocol LabelSwitching (MPLS); Media Access Control (MAC) stacking where a packetcould have multiple MAC addresses, the first MAC address for a substratecomponent, such as a switch, and a second MAC address for a nextcomponent either on the “fast” or the “slow” path; and using NetworkAddress Translation (NAT) devices on both ends of a network in order toredirect traffic into the network, such as by spoofing or altering andestination address for an incoming packing and/or altering an thesource address of an outgoing packet. In some embodiments, the RouteManager generates control signals or messages for coordinating trafficon the substrate network for the various techniques described above.

Virtual Network Route Selection Process

FIG. 7A illustrates a flow diagram for a process 700 of propagatingvirtual routes to a substrate network usable in the example networksdescribed above. The virtual routes can be based on networkconfiguration data provided by a virtual network user, such as costs,component characteristics, preferred routes, and/or the like.

At block 705, the Route Manager module receives user configurationand/or network configuration data, such as, for example, policy basedrouting decisions made by the user. In some embodiments, a userinterface is provided, allowing a user to specify configuration data.The Route Manager can receive the configuration data from a data store,for example, if user configuration and/or network configuration data arestored on the data store after being received on the user interface orotherwise generated. In some embodiments, the configuration data caninclude explicit routing paths through the virtual network. In someembodiments, the configuration data can specify associated costs fortraversing components of the virtual network, such as links and/ornodes. These costs can be based on monetary costs, packet loss rates,reliability rate, and/or other metrics. These costs can be provided bythe user to configure the virtual network provided by the data centeroperator. However, costs and other network configuration data can comefrom the data center operator themselves in addition to or instead offrom the user. For example, the data center operator can use the virtualnetwork to provide feedback to the user on routing costs, such as byassociating monetary use costs for the substrate computing nodes and/orcomponents. In one example, the data center operator can specify a highcost for a high speed network link or high powered computing node sothat the virtual network user can take into account that cost inconfiguring the virtual network.

At block 710, the Route Manager module determines virtual network routesbased on the user configuration and/or network configuration data. Insome embodiments, routing protocols or the route determinationalgorithms of the routing protocols, such as BGP, OSPF, RIP, EIGRP orthe like, can be used to determine virtual routes.

At block 715, the Route Manager determines one or more forwardingentries for substrate network components, such as computing nodes,network translation devices, or the like. As the Route Manager candetermine routing paths and propagate routing decisions to the substratecomponents, the Route Manager can coordinate routing within a datacenter and/or between multiple data centers.

At block 720, the Route Manager transmits the forwarding entries to thesubstrate components. At block 725, the substrate component receives theforwarding entries. The substrate network components can store theforwarding entries in FIB tables or similar structures. Generally, aCommunication Manager on the substrate component receives and processesthe forwarding entry and manages communications of the substratecomponent.

However, as discussed above, network traffic can also be coordinated forsubstrate components without a Communication Manager using instead, forexample, a NAT device or the like. In some embodiments, the RouteManager can send blacklist updates, manage tagging of the packets,generate stacked MAC addresses, or the like.

At block 730, the substrate components route packets received orgenerated according to the stored forwarding entries. Generally, aCommunication Manager on the substrate component manages the packetrouting and refers to the forwarding entries to make forwardingdecisions.

Substrate Network Route Selection Process

FIG. 7B illustrates a flow-diagram for a process 750 for determiningsubstrate routing based on target performance characteristics of theassociated virtual network usable in the example networks describedabove. In some instances, the Route Manager can optionally generate avirtual routing table for the virtual network before determiningsubstrate routing. The virtual routing table can be used to determinevirtual routing paths, allowing optimization of network traffic byselective association of the virtual network components with substratecomputing nodes, such as by taking into account physical location andvirtual network traffic patterns. However, generation of the virtualrouting table is not necessary as the substrate routes can be determinedindependently of the virtual routes, as will be described below. Inaddition, user configuration and/or network configuration data providedby the user can be used to describe the virtual network, without needingto generate a virtual routing table.

At block 755, the Route Manager receives characteristics of thesubstrate nodes and/or node links. The Route Manager can receive thecharacteristics data from a data store. In some embodiments, a userinterface is provided, allowing a user to specify characteristics data.The characteristics can describe such things as monetary costs, networkbandwidth, network security, network latency, network reliability and/orthe like. These characteristics can be used in a cost function fordetermining substrate routing paths. This information can be kept by theRoute Manager or data source accessible by the Route Manager.

At block 760, the Route Manager receives a target network performancefor the virtual network. The target performance can be based on apurchased service level by the user, user history, security data or thelike. For example, a service level purchased by a user can have minimumbandwidth, latency, or quality of service requirements. In anotherexample, a user can be a new customer with an unknown payment historysuch that the user is provisioned on a “slow” virtual network in orderto minimize incurred expenses in case the user fails to pay. In anotherexample, a user identified as carrying dangerous or prohibited traffic,such as viruses, spam or the like, can be quarantined to particularsubstrate components. During quarantine, the virtual network componentscan be assigned to specialized substrate components with more robustsecurity features. For example, the substrate components can haveadditional monitoring functionally, such as a deep-packet scanningability, or have limited connectivity from the rest of the substratenetwork.

At block 765, the Route Manager determines substrate network routesbased on the target network performance and/or characteristics of thesubstrate nodes and/or links. In one embodiment, the Route Manager canuse the characteristic data in a cost function for determining routes.Which characteristic to use or what level of service to provide can bedetermined by the performance criteria or target performance. Forexample, for a “fast” route, the Route Manager can use bandwidth and/orlatency data for the substrate network to generate routes that minimizelatency, maximize available bandwidth, and/or otherwise improve networkperformance.

The Route Manager can re-determine routes as needed based on changes inthe network, the configuration data, and/or the performance level. Forexample, if a user has purchased N gigabits of “fast” routing but hasreached the limit, the Route Manager can generate new routes and shiftthe user to “slow” routing.

At block 770, the Route Manager transmits forwarding entries for one ormore routes to one or more nodes and/or network translation devices. Insome embodiments, the Route Manager determines forwarding entries forthe substrate components and sends those forwarding entries to thesubstrate components on the path. In some embodiments, the Route Managercan send blacklist updates, manage tagging of data packets, and/orgenerate stacked MAC addresses.

At block 775, the Route Manager can optionally update the virtualrouting table based on substrate network routes. By changing the virtualnetwork routing table based on the substrate routes, the virtual networkcan stay logically consistent with the behavior of the substratenetwork. Thus, users won't necessarily be confused by discrepancies inthe virtual routing.

Depending on the embodiment, certain acts, events, or functions of anyof the algorithms described herein can be performed in a differentsequence, can be added, merged, or left out all together (e.g., not alldescribed acts or events are necessary for the practice of thealgorithms). Moreover, in certain embodiments, acts or events can beperformed concurrently, e.g., through multi-threaded processing,interrupt processing, or multiple processors or processor cores or onother parallel architectures, rather than sequentially.

The various illustrative logical blocks, modules, and algorithm stepsdescribed in connection with the embodiments disclosed herein can beimplemented as electronic hardware, computer software, or combinationsof both. To clearly illustrate this interchangeability of hardware andsoftware, various illustrative components, blocks, modules, and stepshave been described above generally in terms of their functionality.Whether such functionality is implemented as hardware or softwaredepends upon the particular application and design constraints imposedon the overall system. The described functionality can be implemented invarying ways for each particular application, but such implementationdecisions should not be interpreted as causing a departure from thescope of the disclosure.

The various illustrative logical blocks and modules described inconnection with the embodiments disclosed herein can be implemented orperformed by a machine, such as a general purpose processor, a digitalsignal processor (DSP), an application specific integrated circuit(ASIC), a field programmable gate array (FPGA) or other programmablelogic device, discrete gate or transistor logic, discrete hardwarecomponents, or any combination thereof designed to perform the functionsdescribed herein. A general purpose processor can be a microprocessor,but in the alternative, the processor can be a controller,microcontroller, or state machine, combinations of the same, or thelike. A processor can also be implemented as a combination of computingdevices, e.g., a combination of a DSP and a microprocessor, a pluralityof microprocessors, one or more microprocessors in conjunction with aDSP core, or any other such configuration.

The steps of a method, process, or algorithm described in connectionwith the embodiments disclosed herein can be embodied directly inhardware, in a software module executed by a processor, or in acombination of the two. A software module can reside in RAM memory,flash memory, ROM memory, EPROM memory, EEPROM memory, registers, harddisk, a removable disk, a CD-ROM, or any other form of computer-readablestorage medium known in the art. An exemplary storage medium can becoupled to the processor such that the processor can read informationfrom, and write information to, the storage medium. In the alternative,the storage medium can be integral to the processor. The processor andthe storage medium can reside in an ASIC. The ASIC can reside in a userterminal. In the alternative, the processor and the storage medium canreside as discrete components in a user terminal.

Conditional language used herein, such as, among others, “can,” “might,”“may,” “e.g.,” and the like, unless specifically stated otherwise, orotherwise understood within the context as used, is generally intendedto convey that certain embodiments include, while other embodiments donot include, certain features, elements and/or states. Thus, suchconditional language is not generally intended to imply that features,elements and/or states are in any way required for one or moreembodiments or that one or more embodiments necessarily include logicfor deciding, with or without author input or prompting, whether thesefeatures, elements and/or states are included or are to be performed inany particular embodiment.

While the above detailed description has shown, described, and pointedout novel features as applied to various embodiments, it will beunderstood that various omissions, substitutions, and changes in theform and details of the devices or algorithms illustrated can be madewithout departing from the spirit of the disclosure. As will berecognized, certain embodiments of the inventions described herein canbe embodied within a form that does not provide all of the features andbenefits set forth herein, as some features can be used or practicedseparately from others. The scope of certain inventions disclosed hereinis indicated by the appended claims rather than by the foregoingdescription. All changes which come within the meaning and range ofequivalency of the claims are to be embraced within their scope.

1. A routing system for determining a routing path for network datapackets through a substrate network associated with a virtual networkhaving virtual components, the routing system comprising: a computinginterface for receiving user-specified characteristics of virtual routesof a virtual network; and a route manager comprising one or morecomputing devices, the route manager configured to: obtain auser-specified virtual route characteristic from the computinginterface, the user-specified virtual route characteristic associatedwith a virtual route identifying one or more virtual components of thevirtual network; associate the user-specified virtual routecharacteristic with at least one computing node, wherein the at leastone computing node is configured to simulate a virtual componentidentified in the virtual route; generate a substrate routing tablebased at least partly on a topology of the substrate network and theuser-specified virtual route characteristic associated with the at leastone computing node, the substrate routing table comprising one or moresubstrate network addresses, the substrate routing table identifyingroutes through the substrate network; generate one or more forwardingentries for the one or more nodes of the substrate network, the one ormore forwarding entries reflecting a substrate route corresponding to anidentified route in the substrate routing table; and communicate the oneor more forwarding entries to the at least one computing node.
 2. Therouting system of claim 1, wherein the user-specified virtual routecharacteristic comprise at least one of a routing cost, monetary cost, apacket loss rate and a communication reliability rate.
 3. The routingsystem of claim 1, wherein the user-specified virtual routecharacteristic comprise user-preferred routing paths between virtualcomponents of the virtual network.
 4. The routing system of claim 1,wherein the at least one computing node of the substrate networkcomprises one or more computing devices connected to one or morecommunications medium.
 5. The routing system of claim 4, wherein theuser-specified virtual route characteristic comprise routing costsbetween nodes of the substrate network for network traffic over thecommunications medium.
 6. The routing system of claim 4, wherein thecommunications medium comprises at least one of a wired and wirelessconnection.
 7. The routing system of claim 1, wherein generating thesubstrate routing table comprises executing a routing protocol topopulate the substrate routing table at least partially based on theuser-specified virtual route characteristic associated with the at leastone computing node.
 8. The routing system of claim 1, wherein the atleast one computing node is associated with multiple virtualcharacteristics corresponding to multiple virtual networks.
 9. Therouting system of claim 1, wherein the at least one computing nodeoperates virtualization software capable of simulating multiple virtualcomponents on the same node.
 10. The routing system of claim 1, whereineach virtual component simulated on the at least one computing node isassociated with a separate set of forwarding entries.
 11. The routingsystem of claim 1, wherein the virtual network spans over multiplecomputing nodes in multiple data centers.
 12. The routing system ofclaim 1, wherein the route manager directs routing for a plurality ofcomputing nodes of the substrate network.
 13. The routing system ofclaim 1, wherein the route manager directs routing for a singlecomputing node of the substrate network, each computing node having anassociated route manager.
 14. The routing system of claim 13, whereinthe route manager operates on the at least one computing node.
 15. Acomputer-implemented method for determining a routing path for networkdata packets through a substrate network associated with an overlaynetwork, the method comprising: by a computing system that comprises oneor more computing devices: in a substrate network comprising a pluralityof nodes and an overlay network at least partially simulated by thesubstrate network, receiving network configuration data specified by auser associated with the overlay network, the network configuration datasupplementary to data included in network data packets, the networkconfiguration data specifying an overlay network characteristic thataffects routing behavior of one or more overlay network components; inresponse to receiving the network configuration data, automaticallyassociating the network configuration data with one or more substratenodes associated with the one or more overlay network components; andadjusting routing in the substrate network based at least in part on thenetwork configuration data associated with the one or more substratenodes.
 16. The method of claim 15, wherein the overlay networkcharacteristic specified by the network configuration data comprises atleast one of a routing cost, monetary cost, a packet loss rate and acommunication reliability rate.
 17. A computer-implemented method fordetermining a routing path for network data packets through a substratenetwork associated with a virtual network, the method comprising: by acomputing system that comprises one or more computing devices: receivingnetwork configuration data supplementary to data included in networkdata packets from one of a plurality of virtual network customers, thenetwork configuration data comprising a characteristic of one or morevirtual components of the virtual network; and in response to receivingthe network configuration data, automatically: associating components ofthe virtual network with one or more nodes of a substrate network, theone or more nodes of the substrate network capable of simulating theoperation of one or more components of the virtual network; associatingthe network configuration data with the one or more substrate nodesassociated with the one or more virtual components of the virtualnetwork; and generating substrate routes through the substrate networkat least partially based on the network configuration data associatedwith the substrate nodes.
 18. The method of claim 17, wherein thenetwork configuration data comprise a cost function specified by a userfor the virtual network.
 19. The method of claim 17, wherein the networkconfiguration data comprise routing metrics between virtual componentsspecified by a user.
 20. The method of claim 19, wherein the routingmetrics comprise at least one of a routing cost, a monetary cost, apacket loss rate and a communication reliability rate.
 21. The method ofclaim 17, wherein the network configuration data corresponds to metricsfor traversing the underlying substrate network.
 22. The method of claim17, wherein generating substrate routes comprises identifying routes byusing the network configuration data associated with the substrate nodeas input to a cost function.
 23. The method of claim 17, wherein thenetwork configuration data comprises routing costs and topology data forthe substrate network and the generated virtual routes minimize thenetwork traffic costs for the underlying substrate network. 24.Non-transitory computer-readable storage medium having stored thereoninstructions that, when executed, direct a computing system to: receivea user-specified characteristic of a virtual route from one of aplurality of virtual network users, the user-specified characteristicidentifying a source and a destination component of a virtual network,the virtual network associated with a substrate network; associate theuser-specified characteristic of the virtual route with at least a firstsubstrate node associated with the source virtual component; identify asubstrate route from the first substrate node to a second substratenode, the substrate route at least partially based on the user-specifiedcharacteristic associated with the first substrate node; and generate acontrol message for the first substrate node, the control messageconfigured to direct network packets associated with traffic from thesource component to the destination component through the substrateroute from the first node to the second node.
 25. The non-transitorycomputer-readable storage medium of claim 24, wherein the virtualnetwork comprises an overlay network over the substrate network.
 26. Thenon-transitory computer-readable storage medium of claim 24, wherein theuser-specified characteristic of the virtual route comprisesuser-defined costs associated with the virtual route.
 27. Thenon-transitory computer-readable storage medium of claim 24, wherein thecontrol message comprises at least one of a forwarding entry, ablacklist update, packet tagging data and MAC stacking data.
 28. Thenon-transitory computer-readable storage medium of claim 24, theinstructions further directing the computing system to: transfer one ofthe source component and the destination component from the second nodeto the first node, the source and destination components simulated onthe same node after the transfer in order to reduce network traffic overthe substrate network between the first node and the second node.